Armature assembly for magnetic-type phonograph pickup

ABSTRACT

An armature assembly for a magnetic-type phonograph pickup having a cord or wire which supports a stylus arm with a magnet mounted thereon, the armature, being supported by the aid of the bending of the cord or wire at one stable point to vibrate uniformly in every direction at that point; and a bearing member of elastic material the compression of which can be adjusted so that at the peak the resonant frequency of the output voltage can be damped, such that the frequency response characteristic of the output voltage can be flattened.

United States Patent [7 2] lnve ntor Shuichi Obata Kyoto, Japan [21 Appl. No. 753,236 [22] Filed Aug. 16, 1968 [45] Patented May 4, 1971 [73] Assignee Matsushita Electric Industrial Co., Ltd.

Oaza Kadoma, Kadoma-shi, Osaka, Japan [32] Priority Aug. 22, 1967, Aug. 22, 1967 [3 3 Japan [3 I 42/72682 and 42/72683 [54] ARMATURE ASSEMBLY FOR MAGNETIC TYPE PHONOGRAPH PICKUP 3 Claims, 8 Drawing Figs.

[52] U.S.Cl ..I79/100.4l M, 179/100.4l (ST) [51] Int. Cl H04r 11/12 [50] Field of Search 179/100.41

References Cited UNITED STATES PATENTS 1,663,884 3/1928 Harrison 179/100.41 3,075,054 l/1963 Cvetko l79/100.4l 3,299,219 l/1967 Madsen l79/l00.41 FOREIGN PATENTS 1,000,035 8/1965 Great Britain 179/100.41 718,099 9/1965 Canada 179/100.4l

Primary Examiner-James W. Moffitt Assistant Examiner- Raymond F. Cardillo, Jr. Attorney-Stevens, Davis, Miller and Mosher PATENIEDHAY 4l9?l 3576.955

4 SHEET10F2 7 PR/OR ART .4 5

' PRIOR ART INVENT OR smucm 089777 wmm a/w ATTOR NE Y3 SHEET 2 BF 2 WWEQQMME FREQUENCY ATTORNEYS ARMATURE ASSEMBLY FOR MAGNETIC TYPE PIIONOGRAPI-I PICKUP This invention relates to improvements in an armature assembly for a magnetic-type phonograph pickup which utilizes a variation in the magnetic flux produced by the vibration of an armature, that is, a vibrator consisting of a stylus, a stylus arm and a magnet.

A pickup of the moving magnet-type which represents one form of electromechanical transducer means and which is widely used for the reproduction of stereophonic sound generally comprises a vibrator consisting of a stylus, a stylus arm and a magnet. In a pickup of this kind, the manner of mounting the vibrator in the body having coils and yokes provided for the detection of a variation in the magnetic flux must be such that the vibrator can freely vibrate relative to the body and yet not' produce any unnecessary vibrations. According to conventional practice, the vibrator has been supported by an annular bearing member made from a flexible and elastic material which surrounds a portion of the vibrator as shown in FIG. 1. In such a structure, the elastic member serves also to damp the vibration of the vibrator. While the above structure has the advantage of being simple and easy to manufacture, it has been defective in that the supporting point of the armature which is expected to lie on .the center of the annular bearing member of flexible and elastic material tends to deviate from the normal location as shown in FIGS. 2a and 2b when the armature is subject to vibration. It has therefore been impossible for the elastic member of such a structure to meet the requirement of uniformly supporting the vibrator over a wide frequency band. The tendency of the supporting point of the armature to migrate to and fro has given rise to a remarkable deterioration of various operating characteristics of the pickup and has especially been a serious problem for the satisfactory reproduction of sound in the high-frequency range.

A frictional force is developed between the sound groove of a record and the stylus and varies continuously with the vibration for the reproduction of sound. The variation of this frictional force has been another cause of deterioration in the operating characteristics because the supporting point of the bearing member of flexible and elastic material tends to oscillate in the longitudinal direction of the vibrator. Another defect involved in the above-described structure has been the impossibility of proper adjustment of the damping effect to be imparted by the elastic member.

It is therefore an object of the present invention to overcome prior defects as specified in the above and to provide an improved armature assembly for moving magnetic-type pickup having a stable supporting point for the vibratory movement and an elastic member whose compression can be finely adjusted.

In accordance with the present invention, the stable supporting point of the amiature can be obtained by supporting the fine cord or wire by means of a slender supporting rod. Furthermore, the damping function can suitably be adjusted by adjusting the finely adjustable damper adjacent to the magnet.

Other objects, features and advantages of the present invention will be readily apparent from the following detailed description of a preferred embodiment taken in conjunction with the accompanying drawings,in which:

FIG. 1 is a sectional view of part of a conventional pickup of the moving magnet-type; FIG. 2a and FIG. 2b are schematic illustrations of the unstable movement of the armature in a conventional pickup shown in FIG. 1;

FIG. 3 is a schematic sectional view of part of the pickup according to the present invention to show the basic structure thereof;

FIG. 4 is a sectional view of an embodiment of the pickup according to the present invention;

FIG. 5 is a perspective view of the pickup shown in FIG. 4,

. with a portion including a stylus shown in a disassembled state;

FIG. 6 is a partly cutaway perspective view showing the internal structure of the pickup shown in FIGS. 4 and 5; and

FIG. 7 is a graphic illustration of the frequency response of the pickup according to the present invention. I

Referring to FIG. 3 in which parts are shown in a simplified form for the ready understanding of the present invention, the pickup comprises a vibrator which includes a stylus 10, a tubular stylus arm 11 of a material such as light metal for transmitting the vibration detected by the stylus l0, and a discshaped magnet 12 of a material such as a platinum-cobalt alloy having a high coercive force so as to produce a variation in the magnetic flux in response to the vibration and thereby to generate an electromotive force representative of the vibration. The magnet 12 is mounted on the stylus arm 11 and is in contact with a bearing member 13 which damps the vibration of the vibrator. The bearing member 13 is made of a flexible and elastic material and is shaped in the form of a ring having a central opening. A very fine cord or wire 14 of material such as a metal or resin extends partly into the vibrator to support the same so that the latter can vibrate on the supporting cord or wire 14. A spacer 15 holds or fixes the supporting cord or wire 14 within a central elongated hole extending along the axis thereof so that the supporting point of the vibrator can be disposed near the magnet 12.

A cylindrical member 16 of nonmagnetic material serves to facilitate the replacement of the assembly consisting of the vibrator and the supporting means therefore and to hold the assembly at the center of the space defined by pole pieces which detect a variation in magnetic flux. Yokes 17 of magnetic material are disposed outside of the cylindrical member 16 in order to detect the variation in magnetic flux due to vibration of the vibrator. The above elements are substantially enclosed in a shielding casing 18 of magnetic material, and a knob 19 is provided to facilitate the dismounting of the cylindrical member 16.

As described above, a portion of the supporting cord or wire 14 is fixed to the interior of the tubular stylus arm 11, by conventional means, such as adhesives or the like, while the remaining portion thereof is substantially fixed within the central axial hole of the spacer 15. The stylus arm 11 and the spacer 15 are very slightly spaced from each other and are connected together by the supporting cord or wire 14, and that portion of the supporting rod 14 connected between the stylus arm 11 and the spacer 15 in the above space serves as a supporting point of the vibrator. The spacer 15 is longitudinally adjustably fitted in the cylindrical member 16 so that it can be fixed relative to the cylindrical member 16 after the elastic member 13 has suitably been compressed. The spacer 15 may be fixed relative to the cylindrical member 16 by cementing or by screwing thereinto a setscrew from one side thereof. The yokes 17 comprise two pairs of pole pieces crossing at right angles, that is, four pole pieces in total. Since each pair of pole pieces forming a power generating section is arranged in slanting relation with respect to the surface of a record, the actual section would not be as seen in FIG. 3, but they are purposely illustrated in a simplified form as shown so that the arrangement thereof can readily be understood.

An embodiment of the present invention is shown in FIGS. 4 to 6 in which like reference numerals are used to denote like parts appearing in FIG. 3. It will be seen that the vibrator and the supporting members therefor including a stylus 10, a stylus arm 11, a magnet 12, an elastic member 13, a supporting cord or wire 14, a spacer l5 and a cylindrical member 16 are substantially surrounded by a shielding casing 18. A reinforcing pipe 26 of magnetic conductor is provided to reinforce the coupling between the stylus arm 11 and the magnet 12, and at the same time, to increase equivalently the length of the magnet and consequently increase the magnetic moment of the magnet 12 under vibration. The compression of the elastic member 13 can be varied by moving the position of the spacer I5 integrally with the vibrator in either direction relative to the cylindrical member I6, and after so adjusting the position of the spacer 15, the spacer 15 is fixed to the cylindrical member 16 by a setscrew 20. The variation in magnetic flux produced by the vibration of the magnet 12 is detected by coils 23 and is converted into an electrical signal which appears as an output voltage across terminals 22 provided in a terminal plate 21. A mounting plate 24 is provided with a plurality of 'mounting holes 27 for mounting the power generating sections on the head of a pickup arm. in FIG. 5, the assembly including the stylus is shown in a state in which it is dismounted from the body portion and is being inserted in the direction of the arrow in order to be mounted in the proper position.

it will be understood from the foregoing description that the armature assembly for a magnetic-type phonograph pickup according to the present invention can eliminate the prior defects, that is, the undesirable to and fro migration of the supporting point of the vibrator resulting from the frictional engagement between the stylus and the sound groove. The armature assembly for the magnetic-type phonograph pickup according to the present invention gives a uniform damping effect in spite of the movement of the vibrator in any direction relative to the supporting point of the vibrator thus ensuring good operating characteristics over a wide frequency range. A further advantage is the remarkable ease of adjusting the compression of the damper.

The'excellent performance of the armature assembly for the magnetic-type phonograph pickup according to the present invention that can be derived from the above advantages will readily be apparent from the frequency characteristic shown in FIG. 7. In FIG. 7, the curves a, b and c represent an excessive frequency response in a high-frequency range due to an insufficient damping effect because the elastic member is not substantially compressed, a preferred flat frequency response up to high frequencies because the elastic member is suitably compressed, and an insufficient response in a high-frequency range due to an excessive damping effect because the elastic member is excessively compressed, respectively. It will be appreciated that the capability of adjustment of the compression of the elastic member by theshifting of the position of the spacer providesan advantage in respect of ease with which a flat frequency response can be obtained.

While a specific embodiment of the present invention hasbeen described above by way of example, the present invention is in no way limited to such a specific embodiment and many changes and modifications may be made therein without departing from the scope of the appended claims.

I claim:

1. An armature assembly for a magnetic-type phonograph pickup comprising a stylus arm, a stylus mounted on one end of said stylus arm, a magnet having a high coercive force fixed to another end of said stylus arm in coaxial relation with said stylus arm, a flexible wire extending at one end into said stylus arm through a central portion of said magnet for supporting said stylus arm thereon, spacer means disposed in spaced relation to said magnet, said spacer means fixedly holding another end portion of said supporting wire, a member having a longitudinal bore passing therethrough in which said spacer means is slidably inserted, and an elastic member mounted, in overhanging relationship on one end portion of said spacer means, adjacent to said magnet for damping a vibration of said magnet, a variation in magnetic flux produced by said vibration of said magnet being detected by coils and converted into an electrical signal as an output voltage.

2. An armature assembly for magnetic-type phonograph pickup according to claim 1, wherein said spacer means is fixed in the position by a setscrew.

3. An armature assembly for magnetic-type phonograph pickup according to claim I, wherein said spacer means is fixed in the position by a cementing material. 

1. An armature assembly for a magnetic-type phonograph pickup comprising a stylus arm, a stylus mounted on one end of said stylus arm, a magnet having a high coercive force fixed to another end of said stylus arm in coaxial relation with said stylus arm, a flexible wire extending at one end into said stylus arm through a central portion of said magnet for supporting said stylus arm thereon, spacer means disposed in spaced relation to said magnet, said spacer means fixedly holding another end portion of said supporting wire, a member having a longitudinal bore passing therethrough in which said spacer means is slidably inserted, and an elastic member mounted, in overhanging relationship on one end portion of said spacer means, adjacent to said magnet for damping a vibration of said magnet, a variation in magnetic flux produced by said vibration of said magnet being detected by coils and converted into an electrical signal as an output voltage.
 2. An armature assembly for magnetic-type phonograph pickup according to claim 1, wherein said spacer means is fixed in the position by a setscrew.
 3. An armature assembly for magnetic-type phonograph pickup according to claim 1, wherein said spacer means is fixed in the position by a cementing material. 